This invention relates to a brush bridge assembly for a permanent-magnet d.c. motor. The bridge assembly includes a carrier plate to which at least two brush guides are secured, each carrying a carbon brush. The carbon brushes are urged by means of biasing springs into contact with a commutator fixedly mounted on a rotor journalling in a cylindrical motor housing.
Brush bridge assemblies are known wherein the carrier plate (base plate) is made of an electrically insulating material and the brush guides are made of metal. The brushes of positive polarity are connected by an insulated cable whose ends are provided with terminals attached by screws to the associated brush components. The biasing springs are coil springs and exert a force on the associated brush with the interaediary of a pivotal lever. The brush is supported (guided) solely by the brush holder. Brush bridge assemblies of this type, because of the great number of individual components, are not adapted for an economical automatic mass manufacture. Furthermore, such known assemblies do not ensure a sufficiently vibration-resistant guidance of the brushes.
German Offenlegungsschrift (application published without examination) 14 63 897 disc loses a collector motor in which too, the brush bridge assembly is formed of a plurality of parts. It is a significant manufacturing disadvantage of the collector motor disclosed therein that one part of the brush bridge assembly is constituted by the motor housing itself which substantially affects the flexibility concerning the assembly and replacement of parts exposed to wear.
Further, brush bridge assemblies for two-pole, permanent-magnet d.c. motors manufactured by injection molding are also known where the components are affixed in a single plane on the base plate. It is a disadvantage of this arrangement that the concentration of heat sources is limited to a single zone.
Also, in German Offenlegungsschrift 27 01 161 a brush bridge assembly is disclosed which has a carrier plate (base plate) made of an insulating material. On a first side of the carrier plate carbon guides, a choke coil and terminal tabs are mounted. The carbon guides have claws which project through the carrier plate. Supporting plates, having transversely oriented projections are inserted between the claws and a second side of the carrier plate. The transverse projections extend through the carrier plate and support coil springs for elastically pressing the carbon brushes (displaceable in the carbon guides) against the commutator of a small motor. A further projection serves as a terminal tab, for example, to establish a plug-in connection through which current is supplied to an associated carbon brush. Holding plates have, on the second side of the carrier plate, U-shaped, integrally formed pockets. The supply of these components to the two plate sides is circumstantial and thus, for an automatic assembly very complicated and expensive apparatus is required. Also, the assembling periods are disadvantageously long.